The present invention relates to an aqueous impregnating emulsion free of organic solvents, which penetrates deeply into dense as well as porous building materials and provides them with good hydrophobic properties, and is also effective in the case of neutral substrates without catalyst.
It is based on mixtures of suitable hydrolyzable and condensable alkoxy-functional silicon resins as well as alkyl alkoxy silanes.
A range of aqueous preparations is known, which had been developed for the hydrophobic impregnation of porous building materials. However, these are associated with a number of disadvantages, which are explained in more detail below:
If the building materials are especially dense, then all the resin-based preparations generally fail with respect to penetration depth, even if they have a relatively low molecular weight. An example of this is provided by the preparations known from EP-A-157 323. They provide the surface of porous building materials with excellent hydrophobic properties with adequate penetration depth. However, in the case of dense building materials, although the surfaces are indeed made hydrophobic, the penetration depth is inadequate. This only provides a time-limited protection against harmful effects from water in such building materials.
Aqueous emulsions of alkyl alkoxyl silanes are preferably used where good penetration depths are required in the case of dense building materials. Such preparations are known, for example, from DE-A-27 51 714, EP-A-234 024 and EP-A-340 816.
Although these preparations, in principle, have acceptable penetrating capacity, they lead to inadequate surface hydrophobia in practice, as demonstrated by heavy wetting during rain showers. Moreover, the desired penetration depth is frequently not achieved. The reasons for this are as follows:
The somewhat problematic stability of the alkyl alkoxyl silanes in emulsion causes condensation products to form, which on the one hand--because of the degree of condensation--are no longer able to penetrate sufficiently deeply, and on the other hand, are not (yet) able to ensure a high degree of surface hydrophobia. If large quantities of buffer substances are added to the emulsions--to prevent premature hydrolysis and to ensure adequate storage stability--, this also affects the desired hydrolysis subsequent to application, since both hydrolysis and condensation--above all in neutral building materials--are greatly inhibited. In particular at summer temperatures, this causes the silanes to evaporate before hydrolysis and condensation can occur. An attempt to counteract this problem by using highly concentrated emulsion leads to wastage of the generally high-quality silanes.
According to DE-A-33 12 911, the disadvantage of the resin-based systems could be overcome by using a mixture of organo-alkoxy siloxanes with a different degree of condensation. These substances are, however, still based on solutions in organic solvents.
An aqueous preparation is disclosed in DE 3 911 479, which comprises a silicon resin together with an alkyl alkoxy silane and a solid with defined surface characteristics. Some of the disadvantages described above do not occur here. However, a problem is posed by the fact that the emulsion concerned additionally has solid particles, and this is not advantageous for the stability of the emulsion. Inadequate physical stability results in a slow hydrolysis and preliminary condensation with the above-mentioned problems. If--as is the case in the disclosed examples--the density of the building materials is relatively low, then serious shortcomings may not be directly ascertained.
If neutral building materials are to be protected at as early a stage as possible against the effects of moisture, then the addition of tin catalysts is recommended to improve effectiveness (Example 4). As is known to one skilled in the art, the addition of a catalyst is critical in so far as it greatly influences the potlife of the ready to use emulsion, which in turn leads to the above-described problems. Moreover, the addition of a catalyst in practice (e.g. on building sites) is carried out under difficult conditions, which results in a higher error rate. It must be noted here that impregnation errors must be avoided at all costs, since they are not immediately recognizable in the majority of cases and therefore may possibly lead to not inconsiderable damage.
None of the named prior publications is concerned with the physical properties of aqueous emulsions used as waterproofing agents.
In the experiments forming the basis of the present invention it was found that it was possible considerably to improve the known waterproofing agents for mineral substances based on aqueous emulsions of silanes and/or siloxane resins, each containing reactive groups, if the dimensions of the emulsified particles and/or droplets lie within a specific, narrowly defined range of magnitude and have a narrow range of particle size. The determined improvement in properties relates to the entire spectrum of properties of importance to such waterproofing agents.
The spectrum of properties includes the stability of the emulsions both in concentrated form and after dilution to the concentration of the application, as well as the hydrophobic effect, i.e. both with respect to the penetration depth of the emulsion prior to hydrolysis and/or condensation, the early water resistance and resistance to water absorption from impregnated mineral building materials.
The known waterproofing agents each constitute a balance with respect to a specific purpose (application in alkaline or neutral mineral building materials, in building materials with higher or lower porosity, in areas with a damp or dry climate, or an evaporation-promoting sunny climate, or a cool climate less favorable to evaporation, and cloudy areas), whereby disadvantages in properties with less serious consequences with respect to the specific purpose of application must be accepted. If such waterproofing agents are provided with the particle size and range according to the invention, the disadvantages accepted hitherto will be reduced, so that their range of use is extended. The range of use may be extended, for example, if use of a catalyst is superfluous, thus increasing the storage stability, or the application of emulsifiers and emulsion stabilizers may be reduced, thus improving the early resistance of the impregnation to rain. Other waterproofing agents suitable for highly porous mineral building materials may also be used for finely porous building materials, if provided with the particle size and range according to the invention.
Apart from the fact that fine-particle emulsions with a narrow range of particle size are generally more stable against coagulation and segregation, there is obviously also a positive influence on the diffusion behavior in the building material as well as the hydrolysis behavior of the silanes and/or the condensation behavior of the siloxane resins.